Back to EveryPatent.com
| United States Patent |
5,789,239
|
|
Eyers
, et al.
|
August 4, 1998
|
Composition and process for the avoidance of slime formation and/or for
the removal of biofilm in water-bearing systems
Abstract
The present invention relates to the use of at least one enzyme component
from the group consisting of carbohydrases, proteases, lipases and glycol
proteases and a short-chained glycol component for the avoidance of slime
formation and/or for the removal of biofilm on surfaces of water-bearing
systems, in particular of industrial process-water systems. The enzyme
component(s) and the glycol component can be added to the water-bearing
system either separately, i.e. at different points, or in the form of an
enzymatic composition containing the enzyme component(s) and the glycol
component.
| Inventors:
|
Eyers; Mark Emile (Tienen, BE);
Van Pee; Kristine Laura Ignatius (Aalter, BE);
Van Poele; Jozef (Borgerhout, BE);
Schuetz; Jurgen Friedrich (Antwerpen, BE);
Schenker; Achim Paul (Eberbach, BE)
|
| Assignee:
|
BetzDearborn Inc. (Trevose, PA)
|
| Appl. No.:
|
759492 |
| Filed:
|
December 4, 1996 |
| Current U.S. Class: |
435/264; 162/161; 210/632; 210/764; 435/267 |
| Intern'l Class: |
D06M 016/00 |
| Field of Search: |
435/264,267
210/632,764
162/161
|
References Cited
U.S. Patent Documents
| 3717550 | Feb., 1973 | Ziffer | 195/63.
|
| 3855142 | Dec., 1974 | Pader et al. | 252/135.
|
| 4092175 | May., 1978 | Martin | 134/42.
|
| 4684469 | Aug., 1987 | Pedersen et al. | 210/632.
|
| 4936994 | Jun., 1990 | Wiatr | 210/632.
|
| 5206026 | Apr., 1993 | Sharik | 424/445.
|
| 5238572 | Aug., 1993 | Hernandez-Mena et al. | 210/632.
|
| 5356800 | Oct., 1994 | Jacquess | 435/188.
|
| 5411666 | May., 1995 | Hollis et al. | 210/632.
|
Primary Examiner: Redding; David A.
Attorney, Agent or Firm: Ricci; Alexander D., Paikoff; Richard A.
Parent Case Text
This is a divisional of application Ser. No. 08/465,214 filed Jun. 5, 1995,
now abandoned.
Claims
We claim:
1. A method for the removal of biofilm and for the prevention of slime
formation on surfaces of a water-bearing system comprising adding to said
water-bearing system an amount, effective for the purpose of an enzyme
component and a glycol component, wherein said enzyme component is a
beta-glucanase and said glycol component is a diethylene glycol.
2. The method according to claim 1, characterized in that the enzyme
component(s) and the glycol component are added to the water-bearing
system at different points.
3. The method according to claim 1, characterized in that the enzyme
component(s) and the glycol component are added to the water-bearing
system in the form of an enzymatic composition according to claims 1 to
10.
4. The method according to claim 3, characterized in that the enzymatic
composition is added in a concentration of 5 to 200 ppm.
5. The method according to claim 1, characterized in that the water-bearing
system is an open or closed industrial process-water system.
6. The method according to claim 5, characterized in that the industrial
process-water system is an open or closed water cycle in a paper factory.
7. The method according to claim 6, characterized in that the water-bearing
system is the white water-bearing cycle of a paper factory.
8. The method according to claim 5, characterized in that the water-bearing
system is a cooling cycle.
Description
BACKGROUND OF THE INVENTION
The present invention relates to the use of at least one enzyme component
from the group consisting of carbohydrases, proteases, lipases and
glycoproteases and a short-chained glycol component for the avoidance of
slime formation and/or for the removal of biofilm on surfaces of
water-bearing systems, in particular of industrial process-water systems.
The enzyme component(s) and the glycol component can be added to the
water-bearing system either separately, i.e. at different points, or in
the form of an enzymatic composition containing the enzyme component(s)
and the glycol-component.
Industrial process- or operating-water systems, such as e.g. open or closed
water-cycle systems of paper factories, in particular cooling-water
systems, offer suitable conditions for the growth of microorganisms, with
the result that a slime known as biofilm is formed on the surfaces of
water-bearing systems. In the case of cooling-water systems in particular,
these biofilm deposits can lead to a reduced heat exchange, damage to the
joints of pipelines and corrosion within the systems. In this way, adverse
effects on process control are possible, which can reduce the efficiency
of the industrial process in question or impair product quality. In
addition to this, biofilm or slime deposits generally lead to higher
energy consumption.
Most affected by an increased biofilm formation are industrial processes
such as the manufacture of pulp, paper, board and textiles. In the case of
paper machines for example, fairly large quantities of water are
recirculated in cycle systems called "white water systems" (primary or
secondary cycle, i.e. white water I or II) (up to ca. 100 to 1000 m.sup.3
water per ton of paper, depending on paper type). The white water, which
contains dispersed pulp, forms an ideal culture medium for the growth of
microorganisms.
Biofilm deposits consist primarily of bacteria, in particular gram-negative
ones, such as Pseudomonas, Acinetobacter and Aerobacter plus
Flavobacterium, Desulfovibrio, Escherichia, Bacillus and Sarcina.
The cell-wall structure of gram-negative bacteria is a factor which
contributes particularly to slime formation. The cell wall consists of
peptidoglycan, which consists of acetyl amino sugars and amino acids plus
an outer membrane composed of proteins, lipopolysaccharides and
lipoproteins. In contrast, the cell wall of gram-positive bacteria is
mostly composed of peptidoglycan and teichonic acids.
Microorganisms also produce extensive slime layers or capsules which vary
in their composition. Apart from a few-exceptions, the slime produced by
the bacteria consists of polysaccharides, such as e.g. dextrans, glucans
or polyuronides. The volume of slime produced by a single bacterium can be
up to many times the volume of the bacterium.
The deposition of the bacterial slimes can most effectively be controlled
with biocides, the effect of these biocides being based on the fact that
they kill off the microorganisms in the operating water and thus prevent
slime production. However, biocides raise many doubts on ecological
grounds and, because of their toxicity, pose considerable dangers when
handled. For this reason, alternative ways of eliminating biofilm were
sought in the past, with particular attention being paid to enzymes.
Although the biofilm matrix can have a heterogeneous composition, it is
primarily built up from polysaccharides. Research in the field of slime
removal has thus concentrated in particular on studies of polysaccharides
(carbohydrases). It was recently found that proteases are effective means
of eliminating biofilm or slime (EP-A-590 746). The proteases most used at
this time are alkaline proteases, derived from various Bacillus strains,
which display advantageous stability properties vis-a-vis bases and are
proteolytically active.
U.S. Pat. No. 4,684,469 describes a process in which the antimicrobial
activity of a biocide is strengthened by a polysaccharide-degrading
enzyme.
U.S. Pat. No. 4,936,994 describes a mixture of cellulase, alpha-amylase and
a protease for the removal of biofilm, and the use of a mixture consisting
of glucanase and protease for slime removal is described in DE 37 41 583.
Described in WO 92/13807 is a process for the removal of biofilm in which a
mixture is used which consists of at least one acid or alkaline protease,
at least one glucoamylase or alpha-amylase and at least one surface-active
agent (i.e. a detergent (surfactant)), which destroys the polysaccharide
material which surrounds the microorganisms adhering to the surfaces of
the water-bearing system.
A feature common to the pure enzyme mixtures or enzymatic compositions used
to date is that they often have to be combined with a biocide in order to
achieve the degree of effectiveness necessary in practice (cf. e.g. U.S.
Pat. No. 5,324,432).
The object of the present invention is therefore to make available a
composition or a process for the avoidance of slime formation and/or for
the removal of biofilm on surfaces of water-bearing systems which avoids
the disadvantages of conventional biocides but achieves their degree of
effectiveness.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 diagrams the structure of the water cycles for the paper machines
used to test the composition according to the invention.
FIG. 2 shows ATP measurements in white water using "bioscan" (cycle 1).
FIG. 3 shows the total bacterial counts in white water (cycle 1).
FIG. 4 shows ATP measurements in white water using "bioscan" (cycle 2).
FIG. 5 shows total bacterial counts in white water (cycle 2).
FIG. 6 shows ATP measurements in white water using "bioscan" (cycle 3).
FIG. 7 shows total bacterial counts in white water (cycle 3).
FIG. 8 shows ATP measurements in white water using "bioscan" (cycle 4).
FIG. 9 shows statistics of black spots/100 ton paper produced before and
during the field trial. The vertical bars represent the day by day
measurements, and the horizontal bars represent the average of a machine
cycle.
FIG. 10 shows statistics of holes/100 ton paper produced before and during
the field trial. The vertical bars represent the day by day measurements,
and the horizontal bars represent the average of a machine cycle.
FIG. 11 shows ATP measurements in the white water, stock and broke.
FIG. 12 shows fungal and yeast counts in the white water, stock and broke.
FIG. 13 shows bacterial cell counts in the white water, stock and broke.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
According to the invention, the object is achieved in that at least one
enzyme component from the group consisting of carbohydrases, proteases,
lipases and glycol proteases and a glycol component of the general formula
R.sup.2 (--O--R.sup.1).sub.n --O--R.sup.3
is added to the water-bearing system, whereby
n is an integer smaller than 10,
R.sup.1 is an alkyl residue with 2 or 3 carbon atoms and
R.sup.2 and R.sup.3 are in each case independently of each other hydrogen,
an alkyl group with 1 to 6 carbon atoms or an aryl group.
The aforementioned alkyl groups of the glycol component can be both linear
and branched. Understood in particular by the term aryl are radicals with
6 to 14 carbon atoms which can contain alkyl substituents. The alkyl or
aryl residues R.sup.1, R.sup.2 and R.sup.3 can in each case be the same or
different.
Within the framework of the present invention, the enzyme component(s) and
the glycol component are preferably added to the water-bearing system at
the same time.
According to a preferred embodiment of the invention, the combined addition
of enzyme(s) and glycol component takes place in the form of a composition
which comprises at least one enzyme component from the group consisting of
carbohydrases, proteases, lipases and glycol proteases and a glycol
component of the general formula
(R.sup.2 (--O--R.sup.1).sub.n --O--R.sup.3
whereby n, R.sup.1, R.sup.2 and R.sup.3 have the meaning given above.
The composition of the invention preferably contains the glycol component
in a concentration of 10 to 80 wt.-% relative to the total composition,
preferably in a concentration of 20 to 60 wt.-%. According to a
particularly preferred version of the invention, the concentration of the
glycol component is 20 to 40 wt.-%.
The quantity of the enzymes in the composition according to the invention
lies between 90 and 1 wt.-%, preferably between 90 and 20 wt.-%, whereby
50 to 20 wt.-% are most preferred (relative in each case to the weight of
the composition in liquid form). The difference to 100 wt.-% of the
composition can be made up by water.
Glucanase (alpha- and beta-glucanase), fucosidase or pectinase are
preferred as enzymes from the class of the carbohydratases. Esperase.RTM.
(serine protease, Novo) or Neutrase.RTM. (metallo-protease, Novo) come
into consideration in particular in the class of the proteases,
Liponase.RTM. (acetylesterase) is particularly suitable as a lipase, and
endo-glycosidase is preferred among the glycol proteases.
While the aforementioned enzymes alone do not remove biofilm sufficiently,
it was surprisingly found that the combination of the enzymes with the
aforementioned low-chained glycol component in the form of a composition
added to the water-bearing system or by simultaneous use (addition) of
enzyme component(s) and glycol component brings with it a dramatic
improvement in slime reduction. The formation of new biofilm is also
greatly reduced. Since even relatively small quantities of the composition
are effective, the quantity of enzyme effectively necessary per liter of
process or operating water can be greatly reduced.
It is known in the prior art that, when the pH value of the water is
neutral, the marked increase in the bacteria cell count gives rise to
increased problems through slime formation, which experience shows can be
controlled only with great difficulty even when biocides are used. It was
able to show according to the invention that, even when the pH value of
the water is neutral, slime formation can be avoided and/or biofilm on the
surfaces of the water-bearing system can be removed if the aforementioned
enzyme component(s) and the glycol component are added to the system
(again either separately or in the form of an enzymatic composition).
According to a particularly preferred embodiment of the invention, an
enzymatic composition is made available which contains beta-glucanase and
diethylene glycol, whereby diethylene glycol is present in a proportion of
10 to 80 wt.-%, preferably 20 to 60 wt.-%, relative to the total
composition. In the composition which is particularly preferred according
to the invention, beta-glucanase is contained in a proportion of 43 wt.-%
and diethylene glycol in a proportion of 25 wt.-%, the difference to 100
wt.-% being made up by water.
The compositions of the present invention develop surprising effectiveness
during the degradation of slime and/or for preventing the formation of
slime on surfaces of water-bearing systems. According to the invention,
water-bearing systems are understood to be in particular industrial
process- or operating-water systems, i.e. open and closed cycles such as
e.g. cooling-water cycles. The compositions according to the invention are
suitable in particular for use in primary, secondary and/or tertiary
cycles of paper factories (i.e. white water I and II, residual waste
water; cf. e.g. Ullmanns Encyklopadie der technischen Chemie, 4th Ed.,
Verlag Chemie, Weinheim, Volume 17, p. 577 et seq.), which are ideal
culture media for microorganisms and in which the formation of slime and
biofilm deposition represents a major problem. The tendency towards slime
formation is at its greatest in the chalk water-bearing cycle, and an
inadequate removal of the biofilm leads to a reduction in paper quality,
to paper machine operating failures and thus to an increase in operating
costs. It has been shown that the composition according to the invention
is suitable to a surprising extent for the elimination of these problems.
The composition of the present invention develops its surprising
effectiveness in numerous other water-bearing systems such as open or
closed water-cycle systems, cooling cycles and the like. As a result of
the degradation of slime and the avoidance of the formation of new slime,
the durability of the water-bearing systems is improved, with the tendency
towards corrosion in particular being greatly reduced.
The present invention also relates to the use of the composition according
to the invention for the avoidance of slime formation and/or for the
removal of biofilm in water-bearing systems, in particular in industrial
process-water systems, in which the composition is added to the system in
a quantity of 5 to 200 ppm relative to the volume of water to be treated.
The compositions of the present invention are ecologically acceptable,
non-toxic and display a clearly higher effectiveness compared with the
known enzyme-containing purification compositions. The replacement of
conventional, toxic biocides is of most advantage for the aforementioned
applications.
Enzymes possess a pH value optimum which is specific to their activity. For
the composition according to the invention, depending on the pH value
present in the water-bearing system, the pertinent optimal enzymes can be
selected for the composition according to the invention.
The invention is explained below with reference to examples.
EXAMPLE
43 wt.-% beta-glucanase, 25 wt.-% diethylene glycol and 32 wt.-% water were
mixed to produce an enzymatic composition (Enzyme formula A).
This composition was used to remove biofilm and to avoid the (re)formation
of slime in the water cycle of two paper machines of a paper factory. The
paper machines had a total capacity of ca. 180,000 tons/year SC paper. The
structure of the water cycles for the paper machines which were used to
test the composition according to the invention is diagrammatically
represented in FIG. 1, where appropriate locations for the metered
addition of enzymatic compositions are marked.
Preparatory Work for Conducting the Field Trial
Installation of the Dosing Apparatus
Several days before the start of the field trial, the Grace Dearborn
DCS3020 dosing apparatus was installed. The following feed locations
(dosing points) were selected:
1. The composition according to the invention EUR8830 was introduced in a
container at the headbox of paper machine PM1 (white water: the dosing
point is designated "SWI" in Table 1 and FIG. 1).
2. The biocide formulation I (containing 18 wt.-%
2,2-dibromo-3-nitrilopropionamide (DBNPA)) was fed into the stock "Debro"
consistency sensor (the dosing point is designated "stock" in Table 1).
3. The biocide formulation II (containing 45 wt.-% Preventol AS 2 and 2
wt.-% dithiol) was fed into the waste "Debro" consistency sensor (the
dosing point is designated "broke" in Table 1).
Two "gamma/5" pumps (ProMinent) were installed for the addition of the
biocide formulations, and a "Vario" pump (ProMinent) was used for the
addition of the composition according to the invention. All the pumps were
calibrated before the start of the practical testing of the composition
according to the invention.
Field Trial
The filed trial was started after the machines had been thoroughly cleaned.
The dosage quantities during the four cycles of the study are shown in
Table 1.
During the first cycle, which lasted 9 days, the composition according to
the invention was added to the white water (4.times.30 minutes per day,
1458 ml/min); the biocides were added into the stock (4.times.30 minutes
per day parallel to the formulation according to the invention 60 ml/min)
and into the broke (3.times.30 minutes per day 75 ml/min). While the
biocide dose was reduced by aprroximately 50% in the second cycle, which
lasted 20 days, the dosage of the composition according to the invention
was not changed (4.times.30 minutes per day, 1458 ml/min). During the
third cycle, which lasted 9 days, the dosage of the composition according
to the invention was reduced by 50% (4.times.30 minutes per day, 730
ml/min). Immediately thereafter, the 4th cycle was started without
addition of biocide into the short cycle (i.e. without addition of D7806),
the added quantity of the formulation according to the invention being
reduced once again by ca. 68% (4.times.30 minutes per day, 500 ml/min).
The papre machine was now treated for 20 days with Enzyme formulation A
only. A small amount of biocide I was used for broke conservation, not
part of the white water.
The outcome of the field trial using the aforementioned enzymatic
composition was monitored as follows:
1. The mixture of the planktonic microorganisms populations was measured
daily by ATP measurements (Bioscan) and total bacteria counts (Petri film
and dipslides) in the white water, in the stock and in the broke. (The ATP
measurements are based on the principle that, during the change from ATP
to AMP in the presence of luciferin and luciferase, in each case defined
quantities of light are emitted per ATP molecule, which are measured by
sensitive photometers). The results of the measurements in the white water
are shown in FIGS. 2-8. There was no significant increase in the bacteria
cell counts or the "relative light unit" (rlu) values. The figures show
the typical microbial activity of a system which displays no problems
attributable to slime formation, i.e. in which the formation of slime is
effectively suppressed.
2. The machine was checked constantly for slime formation and for the
problems associated with it. During the trial, no microbiologically caused
problems were observed in the paper machine. Nor was it necessary in any
case to stop the paper machine because of slime formation.
3. The paper quality was likewise continuously monitored. The statistical
distribution of dark spots and holes in the paper before, during and after
the addition of the composition according to the invention was
ascertained. It was shown that there is no significant difference, in
terms of the number of black spots and holes in the manufactured paper,
compared with the paper quality when using biocides (cf. FIGS. 9 and 10).
4. After a successful field trial over a period of three months, the paper
machine was altered to neutral operation. The paper machine was monitored
as already previously (see above).
It was shown that, even with a neutral pH value, the addition of the
enzymatic composition prevents the occurrence of problems which are
attributable to the formation of slime or biofilm.
The paper machine was constantly monitored, and no biofilm depositions were
observed. The machine looked-very clean and did not have to be stopped
because of microbiological problems, even after the changeover to the
neutral pH value.
The determination of the bacteria cell count, the quantitative recording of
yeasts and fungi and the ATP measurements in the white water, in the stock
and in the broke were carried out at regular intervals. It was found that
the bacteria cell count rises initially, finally to achieve an
equilibrium. The reduction in the proportion of yeasts and fungi is
attributable to the neutral pH value (cf. FIGS. 11 to 13).
Despite the increase in the bacteria cell count, no problems attributable
to slime or biofilm formation were observed when using the enzymatic
composition according to the invention. The number of black spots and
holes did not increase despite the higher bacteria cell counts, which
indicates that the simultaneous addition of the said enzyme component(s)
and glycol component is extremely effective according to the invention as
regards the suppression of slime formation.
Summary of the Results
The use of the composition according to the invention led to results which
are comparable with the use of biocides. The slime deposits were
effectively eliminated (even at neutral pH value) and the formation of new
biofilm was effectively suppressed. The use of the compositions according
to the invention for slime removal thus represents an alternative to the
use of biocides in industrial process-water systems which is effective and
environmentally compatible, in contrast to biocides, and is also
favourable in cost terms.
Holes and cracks in paper machines can be reduced by the compositions
according to the invention, and odour problems as well as microbially
caused blockages in the water-bearing system can be effectively combatted.
TABLE 1
______________________________________
Dosage regime
Cycle PM1
dosing point
product interval ml/min
kg/d
______________________________________
Phase 1 (9 days)
broke biozid I 3 .times. 30
75 7.97
stock biozid II
4 .times. 30
60 8.21
SWI enzyme A 4 .times. 30
1458 192.45
Phase 2 (20 days)
broke biozid I 3 .times. 30
50 5.31
stock biozid II
4 .times. 30
30 4.1
SWI enzyme A 4 .times. 30
1458 192.45
Phase 3 (9 days)
broke biozid I 3 .times. 30
50 5.31
stock biozid II
4 .times. 30
30 4.1
SWI enzyme A 4 .times. 30
730 96.36
Phase 4 (20 days)
broke biozid I 3 .times. 30
50 5.31
stock biozid II
SWI enzyme A 4 .times. 30
500 65.4
______________________________________
Top